class Func():
    def __init__(self,a_list):
        self.a_list = a_list

    def order(self):
        ret = 0
        while True:
            if self.a_list.count(self.a_list[ret]) == 1:
                print(self.a_list[ret])
                break
            else:
                ret += 1


if __name__ == '__main__':
    a_list = [1,1,2,2,3]
    func1 = Func(a_list)
    func1.order()